I don't think you are reading the stock chart right. ORCL has a beta of 1.12 which means it has more volatility than the market as a whole. See image below for a fairly wild stock chart for a year.
I would not truly consider ESPP participation investing, unless you intend to buy and hold the stock. If you intend to sell the stock soon after you are able, it is more speculation.
ESPP's are okay based upon the terms. If the stock was a constant price, and you could sell right away, then an ESPP plan would be easy money. Often, employees are often given a 15% discount to purchase the stock. If you can sell it before any price drop, then you are guaranteed to make 15% on the money invested minus any commissions.
Some employers make ESPP participants hold the stock for a year. This makes such a plan less of a value. The reasons are the stock can drop in price during that time, you could need the money, or (in the best case) your money is tied up longer making the ROI less.
The reasons people invest in stock are varied and is far to much to discuss in a single post. Some of your colleagues are using the ESPP solely to earn the discount in their money.